The fossil record shows that humans are relatively recent arrivals in terms of the geological time scale. Type into your browser: geological time scale humans
Modern genetic analysis shows that over 98% of our DNA is the same as that of chimpanzees. This leads to chimpanzees often being referred to as our “cousins” and the concept that humans evolved from chimpanzees. The idea that humans evolved from chimpanzees is repugnant and unacceptable to many and happily it is not true. What the identity of human and chimpanzee DNA does indicate is that far back in history (6 to 8 million years ago) there was an ancestral species common to both humans and chimpanzees. (Emphasize that 6 million is 6 thousand thousands, plenty of time for incremental changes to occur along two or more different lines.)
Note that the “human family tree” is far from a simple straight line. There were many branches along with many competing hominid species becoming extinct along the way. (Explore other parts of this “Smithsonian National Museum of Natural History site, “What Does It Mean To Be Human”, as you and kids might like, and please post comments or questions.